Visual effects include the various processes by which imagery is created and/or manipulated on film and/or video data. Visual effects are often implemented digitally by processing successive frames of video or scanned film footage. Each frame or set of frames of digitized video is processed by computer algorithms which produce output frames corresponding to the input frames, processed by the effect(s) in question. A collection of one or more effects is defined herein as a look.
Visual effects are usually applied in a computer system, where frames are read from a disk or storage device into the computer, the frames are processed, and written to the same or a different storage device. The effects are controlled either interactively by a user (the video creator), or in batch using a predefined script.
In the interactive case, the video creator uses a “host” application such as Adobe After Effects, Autodesk Flame, Avid Media Composer or similar video editing or compositing applications to (a) identify the frame sequence to apply the effects to, (b) select the effects, (c) set the various parameters which control the final look of the effect, and (d) render the effects by performing the image-processing algorithms on all frames in the sequence. Controls might include blur amount, image shift, strength of color correction, position to apply an overlay image, and many others, as required by the look.